1. Field of the Invention
The present invention relates to a mold, and a process for production of the mold. The present invention relates also to a member having a concavo-convex pattern prepared by use of the mold.
2. Related Background Art
A typical technique for transferring a pattern onto a substrate employed in semiconductor processes is a light exposure technique. In conventional light exposure techniques, integrated circuits of semiconductors have been made finer with a remarkable improvement in the resolution by a fine processing technique for light exposure with a shorter wavelength light source and with the progress in the area of the optical systems. At the moment, exposure of an extremely fine pattern of 100 nm or finer can be conducted by an ArF excimer laser (λ=193 nm). For finer pattern, an F2 excimer laser (λ=157 nm), EUV (extreme UV), X-rays, and electron beams are investigated as the next-generation exposure techniques.
However, the above exposure techniques have the disadvantages of requiring an expensive exposure apparatus, having a low throughput, and the like.
In recent years, a novel microfabrication technique, called a nano-imprinting method, has attracted attention as a microfabrication technique for attaining a high resolution at a low cost. The nano-imprinting method is described, for example, by S. Y. Chou et al.: Appl. Phys. Lett. 67, 3114 (1995) (non-patented document 1). By this technique, a mold having a projection-depression pattern (hereinafter referred to as an concavo-convex pattern) of a nano scale is pressed against a resin layer like a resist on a substrate to transfer the pattern entirely onto the resist, the mold is separated, and a process of etching and lift-off is conducted to form a resist pattern on the substrate. The concavo-convex pattern of the mold is formed by a conventional process by use of an electron beam exposure method or the like. This novel microfabrication technique is simple and productive and is low in production cost due to the repeated use of the mold.
The nano-imprinting method is also applicable in the formation of initiation points in anodization of aluminum. An example is described in Japanese Patent Application Laid-Open No. H10-121292 (patent document 1). In this method, a mold having a regular projection-depression pattern is pressed against a surface of an aluminum substrate to transfer the projections of the mold onto the aluminum substrate as depressions to form physically the initiation points for the anodization, and the aluminum is anodized to form a highly regular porous film. This method enables formation of a fine pattern having an extremely high aspect ratio, or the like, which cannot be formed by a conventional exposure technique. Therefore, this method is useful in many application fields, such as production of magnetic recording media and the like. As described above, the nano-imprinting technique can be superior to conventional exposure techniques. However, even with this technique, for advanced miniaturization of the working pattern, the mold production becomes more difficult. Conventionally, a mold is prepared through steps of applying a resist on a substrate of Si or the like as the base of the mold; forming a resist pattern by exposure to electron beams, X-rays, or the like to form a resist pattern; and transferring the resist pattern to the substrate by selective etching or lift-off. However, the selective dry etching or lift-off becomes more difficult due to the finer exposure pattern, and the exposed pattern is liable not to be transferred precisely onto the substrate, causing a deterioration of the pattern.
To overcome the above disadvantages, Japanese Patent Application Laid-Open No. 2004-285422 (patent document 2), for example, discloses a technique of preparation of a mold, comprising steps of forming an electroconductive metal film directly on a resist pattern; depositing a metal by plating; and removing the resist. This technique is explained by reference to FIGS. 3A, 3B, 3C and 3D. Firstly, resist layer 31 on substrate 30 is patterned by forming fine unevens by a conventional exposure process, such as electron beam lithography and X-ray lithography (FIG. 3A).
Then, on the fine concavo-convex pattern on resist layer 31, layer 32 of an electroconductive metal for electroplating or a catalyst for electroless plating is formed by vacuum deposition, glow discharge, ion-beam sputtering, or a like process (FIG. 3B).
Then, on layer 32 of the electroconductive metal or the catalyst, metal 33 (e.g., nickel) for the mold is deposited by plating (FIG. 3C).
Further, from metal 33 deposited on the surface of the resist, resist layer 31 is removed to obtain mold 34 (FIG. 3D).
By the method of Patent Document 2, a mold is prepared through the above steps.